The last decade was the hottest on record, and yet it wasn't until 2010 that an individual year was hotter than the record-breaking 1998 heatwave. Somehow, global temperatures mysteriously flattened out. The explanation may lie thousands of feet underwater.
Scientists have long been searching for the so-called "missing heat" to explain the disparity between expected rises in global temperatures and the actual, relatively small increases. Based on the rate of greenhouse gas emissions, climate scientists expected the 00's to be warmer than they turned out to be. In fact, our satellites were actually able to monitor the amounts of sunlight entering the atmosphere and radiation leaving it. Way more heat was getting in that getting out, so where was it all going?
Researchers at the National Center for Atmospheric Research now have an answer, thanks to a series of computer simulations that strongly suggest the extra, unaccounted for heat can be found deep underwater at depths below a thousand feet. All this heat energy is being stored in the ocean depths, masking the true temperature buildup for several years, perhaps for as long as a decade.
What these findings essentially suggest is that, while long-term temperature increases remain constant, Earth can still experience long hiatuses in which temperatures flatten out. In one simulation, for instance, the temperature rose 2.5 degrees Fahrenheit between 2000 and 2100, but there were two decade-long periods in which temperatures didn't rise at all. We appear to be right at the end of one of those hiatuses.
Lead author Gerald Meehl adds:
"We will see global warming go through hiatus periods in the future. However, these periods would likely last only about a decade or so, and warming would then resume. This study illustrates one reason why global temperatures do not simply rise in a straight line."
There's still a lot we don't know here. Indeed, we still have very little direct evidence to back up the simulation - while scientists have long suspected the deep ocean acts as a heat repository, it's very difficult to collect reliable data at those levels. The simulations suggest that ocean temperatures at below 1,000 feet should have risen at a rate 18% to 19% more than expected during these hiatus periods. What that means for the overall health of the oceans and its wildlife is still anyone's guess.
Researcher Kevin Trenberth sums up the basic uncertainty about all this:
"This study suggests the missing energy has indeed been buried in the ocean. The heat has not disappeared, and so it cannot be ignored. It must have consequences."
The basic story hasn't changed here - temperatures are rising, and it's very much in our best interest (not to mention that of the planet) for us to do something about it. All we have now is one more factor to consider. But just how the ocean depths really fit into the larger story of climate change is still something we need to figure out.